The present invention relates to a rubber laminate in which a FKM layer and a NBR layer are bonded together through vulcanization. It is suitable for an automotive fuel hose and fuel pump diaphragm. "FKM" and "NBR" used in this specification stand for fluororubber and nitrile rubber, respectively. "PHR" denotes an outer percentage based on the amount of rubber or polymer.
Being superior in heat resistance, chemical resistance, aging resistance, low-temperature resistance, and oil and fuel resistance, FKM is considered as a promising raw material for a fuel hose, fuel pump diaphragm, and chemical-resistant hose and packing. However, its usage is limited because of its high price. It costs 10 to 20 times higher than general-purpose rubber such as NBR. One way of overcoming this disadvantage is to use FKM in combination with NBR. For example, where FKM is used as a raw material for a fuel hose, the base layer is made of NBR, which is a general-purpose rubber having a comparatively good oil resistance, and the layer required to have a high performance is made of FKM, and the two layers are bonded together through vulcanization. In actual, however, the bonding of the two layer is difficult to achieve by the ordinary method. This holds true particularly of an FKM layer made of a rubber compound for peroxide vulcanization. In the meantime, FKM of peroxide vulcanization type cures faster and more densely than FKM of polyamine-polyol vulcanization type. Therefore, it provides a low compression set without secondary cure.
In order to improve the bonding between a FKM layer and a NBR layer, there was proposed an unvulcanized NBR compound containing a metal oxide such as magnesium oxide and silica, as disclosed in Japanese patent publication Nos. 49391/1982 and 33304/1984. This method, however, does not provide a sufficient bond strength between the two layers.